1. Field of the Invention
This invention relates to a resist composition and a process for producing a resist composition comprising an alkali-soluble resin, a radiation-sensitive compound and a solvent, said composition being sensitive to radiations such as ultraviolet ray, far ultraviolet ray, X ray, electron beam, molecular beam, .gamma. ray, synchrotron radiation, proton beam and the like. More particularly, this invention relates to a process for producing a resist composition suitable for use in the preparation of integrated circuits, as well as to said resist composition.
2. Description of the Related Art
With the appearance of highly integrated LSI, the design geometrics for integrated circuits has become finer from about 1 .mu.m to about 0.5 .mu.m. The resist compositions used in such fine processing are requested to have not only excellent fundamental performances such as resolution, sensitivity, profile, coating characteristics, depth of focus, etc. but also a low number of relatively large undissolved particles present in the composition in the stage just after production and a good storage stability, which means that the number of such relatively large undissolved particles does not increase markedly even if the composition is stored for a long period of time. Thus, if a resist composition containing a large number of such relatively large, undissolved, visually unobservable particles in a large number is used, a substrate etched with a resist pattern given from such a resist composition often forms pin-holes in the area covered by the resist pattern and thereby the production yield of integrated circuit is decreased.
As the solvent for resist compositions, cellosolve type solvents such as ethylcellosolve acetate, etc. relatively superior in the dissolving power on radiation-sensitive compounds have generally been employed. When a cellosolve type solvent is used, however, the number of the relatively large undissolved particles in the resist composition gradually increases until it reaches an abnormally high level after a long-term storage, even though it was on a lower level just after the composition was produced. Recently, such cellosolve type solvents are being replaced by ethyl lactate or ethyl pyruvate. If these solvents are used, however, the number of relatively large undissolved particles in a resist composition just after production is greater than that given by the use of cellosolve type solvents, and the number of undissolved particles after a long-term storage is further greater than that just after production. As has been mentioned above until now, it has been impossible to produce a resist composition having low levels of relatively large undissolved particles just after production and excellent in storage stability.